Analyte Test Instrument Having Improved Versatility

ABSTRACT

An analyte test instrument that has a test strip circuitry that can be configured using information provided by a calibration strip to perform assays with test strips having two electrodes and test strips having three electrodes. The analyte test instrument of this invention comprises:
         (a) a test port for receiving a test strip;   (b) a microprocessor for executing instructions downloaded into the analyte test instrument;   (c) a test strip circuit capable of having a plurality of configurations, the configurations being set by the microprocessor, whereby an assay can be performed using the test strip.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to analyte test instruments that performelectrochemical assays on biological samples. More particularly, theinvention relates to analyte test instruments that can performelectrochemical assays by using different modes of operation.

2. Discussion of the Art

Electrochemical assays for determining the concentrations of analytes insamples comprising complex mixtures of liquids have been developed.

Such electrochemical assays can be performed with test strips, i.e.,biosensors in the form of strips. Test strips can function in aninvasive manner (i.e., as probes that come into contact with a bodyfluid, such as whole blood or subcutaneous fluid). Test strips canfunction in a non-invasive manner (i.e., as strips that come intocontact with blood withdrawn by a syringe or a lancing device). Inparticular, test strips for biomedical applications (e.g., whole bloodanalyses) have been developed for the determination of glucose levels inbiological samples.

An analyte test instrument is an instrument can be used to performelectrochemical assays to determine the concentration of an analyte(e.g., glucose) in a biological sample (e.g., blood). To operate such aninstrument, a user inserts a test strip into a test port in theinstrument. The instrument displays a “ready” indication to the user andallows sufficient time for the user to deposit a biological sample onthe test strip. When a sufficient quantity of the sample reaches theworking electrode of the test strip, an electrochemical reaction occurs.The reaction produces an electrical response, such as a change incurrent. The electrical response is detectable by the analyte testinstrument. The analyte test instrument converts the detected signalinto data that corresponds to information relating to the analyte anddisplays the information to the user. The instrument may be able tostore a series of such measurements and provide the stored informationto the user via a display or to an external processor via a data link.

All commercially available electrochemical assays employing test stripsfor determining the concentration of glucose employ test strips havingtwo electrodes. See, for example, WO 99/19507, incorporated herein byreference, which describes a test strip having two electrodes. In a teststrip having two electrodes, the test strip has (1) a working electrodeand (2) a dual-purpose reference/counter electrode. The reaction thattakes place at the working electrode is the reaction that is required tobe monitored and controlled. The second electrode is called adual-purpose reference/counter electrode because this electrode acts asa reference electrode as well as a counter electrode. No current passesthrough an ideal reference electrode, and such an electrode maintains asteady potential; current does pass through a dual-purposereference/counter electrode, and thus, the dual-purposereference/counter electrode does not maintain a steady potential duringthe measurement. At low currents and/or at short durations of time formeasurement, the shift in potential is small enough such that theresponse at the working electrode is not significantly affected, andhence the dual-purpose reference/counter electrode is designated adual-purpose reference/counter electrode. The dual-purposereference/counter electrode continues to carry out the function of acounter electrode; however, in this case, the potential that is appliedbetween the dual-purpose reference/counter electrode and the workingelectrode cannot be altered to compensate for changes in potential atthe working electrode.

Electrochemical assays employing test strips having three electrodesemploy a test strip having (1) a working electrode, (2) a referenceelectrode, and (3) a counter electrode. See, for example, U.S. Ser. No.10/062,313, filed Feb. 1, 2002, incorporated herein by reference. As inthe test strip having two electrodes, the reaction that takes place atthe working electrode is the reaction that is required to be monitoredand controlled. The functions of the reference electrode and the counterelectrode are to ensure that the working electrode actually experiencesthe conditions desired, i.e. the correct potential intended to beapplied. The function of the reference electrode is to measure thepotential at the interface of the working electrode and the sample asaccurately as possible. In an ideal situation, no current passes throughthe reference electrode. The function of the counter electrode is toensure that the correct potential difference between the referenceelectrode and the working electrode is being applied. The potentialdifference between the working electrode and the reference electrode isassumed to be the same as the desired potential at the workingelectrode. If the potential measured at the working electrode is not thepotential desired at the working electrode, the potential that isapplied between the counter electrode and the working electrode isaltered accordingly, i.e., the potential is either increased ordecreased. The reaction at the counter electrode, as measured by thecurrent, is also equal and opposite to the charge transfer reaction, asmeasured by the current, occurring at the working electrode, i.e., if anoxidation reaction is occurring at the working electrode then areduction reaction will take place at the counter electrode, therebyallowing the sample to remain electrically neutral.

An analyte test instrument designed for test strips having twoelectrodes could not be used if an assay employing a test strip havingthree electrodes needs to be performed. The user would have to use aseparate analyte test instrument. If the user wanted to perform a set ofassays that required strips having two electrodes and a set of assaysthat required strips having three electrodes, these assays could not beperformed on the same analyte test instrument.

An analyte test instrument for electrochemical assays often requires theuser to calibrate the instrument for each batch of test strips. U.S.Pat. No. 5,366,609, incorporated herein by reference, describes acalibration technique that requires a read-only-memory (ROM) key foroperation and calibration of an analyte test instrument. A ROM key isinserted into a port (i.e., the ROM key port) that is distinct from theport for a test strip (i.e., the test port). A test strip is insertedinto the test port after the ROM key is inserted into the ROM key port.The ROM key must remain in the ROM key port during both the calibrationand the operation of the instrument. The ROM key contains specific data,including algorithms, for carrying out procedures for determining theconcentration of an analyte in a biological sample applied to one of abatch of test strips associated with the ROM key. The data stored in theROM key include measurement delay times, incubation times, the number ofmeasurements to be taken during a measurement period, various thresholdsagainst which voltage levels can be compared, values of excitationvoltage levels applied to the strip during a test procedure, glucosevalue conversion factors, and a variety of failsafe test thresholdvalues. In addition, the ROM key can contain some or all of the code forthe microprocessor that controls the performing of the assay. Amicroprocessor in the analyte test instrument uses the algorithms, theconversion factors, and the code provided by the ROM key as needed.

U.S. Pat. No. 6,377,894, incorporated herein by reference, describes aninstrument requiring a ROM key for operation and calibration of theinstrument. The ROM key is inserted into the test port of the instrumentand data is downloaded from the ROM key by the instrument and stored inthe memory of the instrument. The ROM key contains data needed forcarrying out procedures for determining the concentration of an analytein a biological sample applied to a test strip. The ROM key is removedso that test strips can be inserted into the test port to performassays. Different ROM keys can be inserted into the instrument toprovide data for the testing of different analytes on the sameinstrument. The instrument can communicate with the ROM key to determinethe analyte for which the ROM key contains information. Calibrationinformation can be stored in different locations in the memory of theinstrument for each analyte the instrument is capable of testing. When atest strip is inserted into the test port, the instrument has theability to recognize which analyte is being tested. The microprocessorin the instrument then recalls the instructions for carrying outprocedures for determining the concentration of that analyte, and theinstrument then performs the appropriate test.

The aforementioned patents do not describe how the electrical circuitryof the instrument can be reconfigured so that analytical tests thatrequire different circuit configurations can be performed on the sameinstrument. The aforementioned patents do not describe how storedinformation relating to the configuration of the electrical circuitry ofthe instrument can be modified when an assay for a specific analyteneeds to be modified. The aforementioned patents do not describe howstored information can be used to reconfigure the electrical circuitryof the instrument while a test, strip is being used. Accordingly, itwould be desirable to provide an analyte test instrument that addressesthe foregoing deficiencies.

SUMMARY OF THE INVENTION

In one aspect, this invention provides an analyte test instrument thathas test strip circuitry that can be placed into differentconfigurations by means of information provided by a calibration stripto perform assays with test strips having two electrodes and test stripshaving three electrodes. In another aspect, this invention providesmethods for using the analyte test instrument to perform assays withtest strips having two electrodes and test strips having threeelectrodes. The analyte test instrument of this invention comprises:

-   -   (a) a test port for receiving a test strip;    -   (b) a microprocessor for executing instructions downloaded into        the instrument; and    -   (c) a test strip circuit capable of having a plurality of        configurations, the configurations being set by the        microprocessor, whereby an assay can be performed using a test        strip that has been inserted into the test port.

In preferred embodiments, the analyte test instrument further includes amemory for storing instructions and information required for theoperation of the instrument. However, in other embodiments, the memorycan be removably attached to the instrument, as described previously inU.S. Pat. No. 5,366,609.

In one embodiment, the invention provides an analyte test instrumentthat can perform assays on a variety of different analytes. In order toperform these assays, a calibration strip is inserted into the testport. After communication is established between the calibration stripand the analyte test instrument, information (i.e., data or programs orboth) involving the method(s) for performing the assay(s) are downloadedfrom the calibration strip, and, if the analyte test instrument has amemory, preferably stored in the memory of the analyte test instrument.In the analyte test instrument having a memory, the information isstored in the analyte test instrument after the calibration strip isremoved. The stored information specifies whether the method(s) of theassay(s) requires a test strip having two electrodes or test striphaving three electrodes.

In the performance of an assay, a test strip is inserted into the testport, and the identity of the assay is indicated, preferably by means ofa pattern of conductive material applied to a major surface of the teststrip, preferably the major surface that does not support theelectrodes. The analyte test instrument then determines from thedownloaded information whether the assay calls for a test strip havingtwo electrodes or for a test strip having three electrodes. Theappropriate electrical switches in the test strip circuit of the analytetest instrument are then opened or closed to establish the configurationof the test strip circuit appropriate for the test strip utilized in theassay, that is, a test strip having two electrodes or a test striphaving three electrodes. A sample to be analyzed, typically a biologicalsample, is then applied to the test strip, and a reaction that generatesan electrical response occurs. The electrical response is detected andmeasured by the analyte test instrument, and the concentration of theanalyte tested is determined by means of the downloaded calibrationinformation. The analyte test instrument then displays the concentrationof the analyte. Assays that call for a test strip having two electrodesand assays that call for a test strip having three electrodes can beperformed on the same analyte test instrument.

In another embodiment, the analyte test instrument of this inventionfeatures the capability of changing the method for performing an assayto determine the concentration of a particular analyte. In order tochange the method for performing the assay, a new calibration strip isinserted into the test port. The instructions for the performing the newmethod of the assay for the particular analyte are then downloaded tothe analyte test instrument, and, if the analyte test instrument has amemory, preferably stored in the memory of the analyte test instrument.When the test strip is inserted into the test port, the identity of theassay is determined. The appropriate electrical switches in the teststrip circuit of the analyte test instrument are then opened or closedto establish the appropriate circuit configuration for the test striputilized in the assay, that is, a test strip having two electrodes or atest strip having three electrodes. The circuit configurations are basedon the information from the calibration strip most recently downloadedto the analyte test instrument. The same analyte test instrument can beused to perform an assay even if the test method is changed oneemploying a test strip having two electrodes to one employing a teststrip having three electrodes, and vice versa.

In another embodiment of this invention, the analyte test instrument canemploy both a two-electrode mode and a three-electrode mode during thesame assay. The expression “two-electrode mode” refers to the test stripcircuitry employed for operating an analyte test instrument with a teststrip having two electrodes. The expression “three-electrode mode”refers to the test strip circuitry employed for operating an analytetest instrument with a test strip having three electrodes. Theinformation previously downloaded from the calibration strip, and,preferably, stored in the memory of the analyte test instrument,specifies what portion of the assay employs a test strip circuitconfiguration in a two-electrode mode and what portion of the assayemploys a test strip circuit configuration in a three-electrode mode. Atest strip is inserted into the test port, and the identity of the assayis indicated, preferably from a pattern of conductive material that hasbeen applied to a major surface of the test strip, preferably the majorsurface that does not support the electrodes. The analyte testinstrument then determines from the aforementioned downloadedinformation whether the assay requires a test strip circuitconfiguration in a two-electrode mode or a test strip circuitconfiguration in a three-electrode mode at the start of the assay. Theappropriate electrical switches in the analyte test instrument are thenopened or closed to establish the appropriate electrode mode. A sampleto be analyzed, typically a biological sample, is then applied to thetest strip, and a reaction that generates an electrical response occurs.During the performance of the assay, the appropriate electrical switchesin the analyte test instrument are then opened or closed to establishthe test strip circuit configuration for the appropriate electrode mode,which is a different electrode mode than was used at the start of theassay. The electrical response is detected and measured by the analytetest instrument, and the concentration of the analyte is determined bymeans of the downloaded calibration information. The analyte testinstrument can then display the concentration of the analyte.

One example wherein the test strip circuit configuration is switchedduring an assay involves an assay in which it may be preferred to use atest strip having three electrodes for the advantages provided by theuse of a test strip having three electrodes, such as, for example,improved control of voltage at the working electrode. However, it may bedesired to exclude the working electrode of the test strip having threeelectrodes during the sample detection phase of the assay. In this case,the test strip circuit for the two-electrode mode is preferred duringthis sample detection phase of the assay. Accordingly, test stripcircuit configurations for both the two-electrode mode and thethree-electrode mode are desired within the course of an assay. It isassumed that an assay involves operational steps beginning with theinsertion of the test strip into the analyte test instrument andobtaining the result of the assay.

The analyte test instrument of this invention makes it possible for theuser to perform assays with test strips having two electrodes and teststrips having three electrodes with the same instrument. The analytetest instrument of this invention makes it possible for an assay to bemodified without having to discard the instrument. The analyte testinstrument of this invention makes it possible for the mode of operationto change during the performance of an assay without intervention fromthe user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of an analyte testinstrument suitable for use in this invention.

FIG. 2 is a block diagram that illustrates electronic components of ananalyte test instrument suitable for use in this invention.

FIG. 3A is a perspective view of a test strip that is suitable for usewith the analyte test instrument of this invention.

FIG. 3B is a perspective view of a calibration strip that is suitablefor use with the analyte test instrument of this invention.

FIG. 4A illustrates a top plan view of test strip that is suitable foruse with the analyte test instrument of this invention.

FIG. 4B illustrates a bottom plan view of test strip that is suitablefor use with the analyte test instrument of this invention.

FIG. 5 is a flow chart illustrating a method for calibrating the analytetest instrument of this invention.

FIG. 6 is a flow chart illustrating a method for calibrating the analytetest instrument of this invention.

FIGS. 7A, 7B, and 8 are schematic diagrams that illustrates a test stripcircuit that can be used to perform assays with two different types oftest strips.

DETAILED DESCRIPTION

As used herein, the expression “test strip having two electrodes” andother expressions relating to tests strips having two electrodes referto test strips that have a working electrode and a dual-purposereference/counter electrode. The expression “test strip having threeelectrodes” and other expressions relating to tests strips having threeelectrodes refer to test strips that have a working electrode, a counterelectrode, and a reference electrode, the reference electrode beingseparate from the counter electrode. A “test strip having twoelectrodes” can have one or more additional electrodes, so long as thestrip has a dual-purpose reference/counter electrode that performs thefunctions of both a reference electrode and a counter electrode. Forexample, a test strip having two electrodes can have a triggerelectrode, which is an electrode that detects when a sufficient quantityof sample has been applied to the test strip. A “test strip having threeelectrodes” can have one or more additional electrodes, so long as thetest strip has one electrode for performing the function of a referenceelectrode and another electrode for performing the function of a counterelectrode. For example, a test strip having three electrodes can have adummy electrode, which is an electrode that is similar to the workingelectrode, but lacks the substance that reacts with the analyte (see,for example, U.S. Pat. No. 5,628,890), or a trigger electrode dedicatedto the sole function of detecting when a sufficient quantity of samplehas been applied to the test strip (see, for example, U.S. Pat. No.5,582,697). As stated previously, all commercially availableelectrochemical test strips for determining the concentration of glucoseemploy two electrodes—(1) a working electrode and (2) a dual-purposereference/counter electrode. As stated previously, electrochemicalsystems having three electrodes employ (1) a working electrode, (2) areference electrode, and (3) a counter electrode.

Electrochemical systems employing test strips having three electrodeshave the requirement that little or no current pass between the workingelectrode and the reference electrode. This requirement is achieved byusing high impedance operational amplifiers in the electrical circuitsof these systems. High impedance operational amplifiers are expensive;consequently, electrochemical systems that perform assays with teststrips having three electrodes are expensive. These expensive systemsare generally used only in research and are not practical from a coststandpoint for use by diabetics for glucose monitoring at home.

A test strip having three electrodes would be preferred in anyelectrochemical measurement that involves the application of an externalvoltage and measurement of current. However, due to constraints ofsample volume (lower volume requirements), all electrochemical teststrips commercially available use only two electrodes. Precise controlof the voltage difference between the working electrode and thereference electrode must be maintained, but such control is difficult toachieve in a test strip having two electrodes. In known analyte testinstruments, the electrical components of an analyte test instrumentdesigned for test strips employing two electrodes would not operate withtest strips employing three electrodes.

Referring now to FIG. 1, an analyte test instrument 100 comprises ahousing 102, which contains the electrical and electronic components ofthe analyte test instrument. The analyte test instrument 100 comprises atest port 110, a push button 120, and a display 130. The test port 110is a multi-purpose test port, which comprises a slot into which a userinserts test strips and calibration strips. The test port 110 comprisesa slot assembly capable of receiving a strip, such as a test strip or acalibration strip. The test port 110 can have a plurality of electricalcontacts capable of electrically engaging such a strip when the strip isinserted into the test port 110. The push button 120 allows the user tocontrol the analyte test instrument 100. In particular, the push button120 is used to turn the instrument on and off, to recall informationstored in the instrument, to respond to messages displayed, and to setsome of the configuration control parameters for the instrument. Thepush button 120 can also provide access to menus generated by softwarecontained in the analyte test instrument 100. The display 130 is adevice that gives information in a visual form. The display 130 istypically a screen. The information given typically includes, but is notlimited to, test results, messages to the user, information stored inthe memory of the analyte test instrument.

In one embodiment, one or more replaceable batteries (not shown)installed via a battery compartment at the rear of the analyte testinstrument 100 (not shown) provide power for the analyte test instrument100. It should be understood, however, that any source of power capableof providing a suitable direct (DC) voltage can provide power to theanalyte test instrument 100.

FIG. 2 is a block diagram that shows the interrelationship among theelectronic components of an analyte test instrument 100. In addition tothe aforementioned test port 110, push button 120, and display 130, allof which are accessible from the exterior of the analyte test instrument100, the analyte test instrument 100 comprises a processing circuit 210,at least one device circuit 212, at least one test strip circuit 214, amicroprocessor 216, and a memory 218.

The purpose of the processing circuit 210 is to enable a strip that isengaged in the test port 110 to communicate with the microprocessor 216and the memory 218. For example, the processing circuit 210 can sendsignals to the test port 110 to determine the identity of the stripinserted therein, i.e., to determine whether the strip is a calibrationstrip or a test strip.

The device circuit(s) 212 and the test strip circuit(s) 214 can compriseanalog, digital, or mixed-signal circuits, application-specificintegrated circuits (ASICS), and passive and active electricalcomponents. The device circuit(s) 212 can perform various electricalfunctions required by the analyte test instrument 100, such as drivingthe display function 130 and the clock functions for a microprocessor216. In other words, the device circuit(s) carries instructions from themicroprocessor 216 to various functional components of the analyte testinstrument 100 so that these components can perform their intendedfunctions. Test strip circuit(s) 214 can perform analog-to-digital (A/D)conversion of signals received at the test port 110 from a test stripand can perform digital-to-analog (D/A) conversion of signals receivedfrom the microprocessor 216. In other words, the test strip circuit(s)transmits information between the microprocessor 216 and the test strip.For example, the test strip circuit(s) is used to ensure that the propervoltage is being applied to the test strip and that the proper value ofcurrent generated at the test strip is being measured by themicroprocessor 216.

The microprocessor 216 is an integrated circuit that contains the entirecentral processing unit of a computer. The memory 218 is a unit of acomputer that preserves information for the purpose of retrieval. Suchinformation may include, but is not limited to, measurement delaytime(s), sample incubation time(s), number of measurements to be takenduring an assay, threshold(s) against which voltage level(s) can becompared, value(s) of excitation voltage level(s) applied to a teststrip during an assay, analyte value conversion factors, failsafe assaythreshold value(s), and configurations of circuitry of the analyte testinstrument.

In a preferred embodiment, the memory 218 comprises at least 1K ofrandom access memory (RAM). In more preferred embodiments, the memory218 has sufficient additional capacity to store a multiplicity of assayresults.

Instrument software 220 is responsive to information received at thetest port 110 from a calibration strip. The instrument software 220 usesthe information received to control the operation of the analyte testinstrument 100. The instrument software 220 also controls operations ofthe analyte test instrument 100 that are independent of informationintroduced or generated at the test port 110. For example, theinstrument software 220 can enable the user to recall assay results andassay information, can provide various warning, error, and promptingmessages, can permit setting of date and time, can control transmissionof data to external devices, can monitor power level or battery level orboth, and can provide indications to the user if power drops below aspecified level.

In the embodiment illustrated in FIG. 2, the test port 110 includes sixelectrical contacts, which are labeled IDENT1, IDENT2, IDENT3, SENS1,SENS2, and SENS3. When a strip is inserted into the test port 110, themajor surfaces of the strip engage the electrical contacts of the testport 110, thereby enabling the analyte test instrument 110 to identify apattern of conductive material on the top major surface of the strip, onthe bottom major surface of the strip, or on both major surfaces of thestrip. In a preferred embodiment, the pattern of conductive material onan inserted strip that interacts with the electrical contacts IDENT1,IDENT2, and IDENT3 indicates whether the inserted strip is a calibrationstrip or a test strip. This embodiment is shown in FIGS. 4A and 4B,which will be described later. If the inserted strip is a test strip,the type of analyte to be determined by the assay to be performed withthe test strip is also identified (e.g., glucose, ketone bodies, etc.).The engagement of the electrical contacts and the strip identificationprocess are described in more detail in U.S. Pat. No. 6,377,894,incorporated herein by reference. The electrical contacts labeled SENS1,SENS2, and SENS3 relate to the electrodes that are involved inperforming analytical tests.

FIG. 3A illustrates in more detail a test strip 230. A plurality ofelectrical contacts 232 is provided at the end 234 of the test strip 230that is inserted into the test port 110. Upon insertion of the teststrip 230 into the test port 110, the electrical contacts 232 contactthe electrical contacts SENS1, SENS2, and SENS3. Typically, a sample,e.g., a drop of blood, undergoing the assay is placed for testing on thereaction area 236 of the test strip 230. The reaction area 236 is thearea where the sample contacts the electrodes of the test strip 230(i.e., the working electrode and the dual purpose reference/counterelectrode in the strip having two electrodes and the working electrode,the reference electrode, and the counter electrode in the strip havingthree electrodes). When a sufficient quantity of sample is deposited onthe reaction area 236, an electrochemical reaction occurs, whereby aflow of electrons produces an electrical response, such as a change incurrent. The response is detectable by the analyte test instrument 100.The analyte test instrument 100 converts the detected response into datathat is correlated with information relating to the analyte and displaysthe information to the user.

FIG. 3B illustrates a ROM-type calibration strip 240. In one embodiment,a ROM-type calibration strip 240 is associated with a package (notshown) of test strips 230. A plurality of electrical contacts 242 isprovided at the end 244 of the calibration strip 240 that is insertedinto the test port 110. In one embodiment, the calibration code 246 andmanufacturing lot number 248 are printed on the calibration strip 240and are visible to the user. In another embodiment, the lot number isstored in a read-only-memory (ROM) 250 in binary coded decimal (BCD)format.

The ROM 250, which is in electrical communication with the electricalcontacts 242, encodes information relating to algorithm(s) forprocessing data obtained in an assay with a test strip. The ROM 250 canalso encode information relating to the calibration code 246 andmanufacturing lot number 248 as well as other parameters, as describedin U.S. Pat. No. 6,377,894, incorporated herein by reference. The assaysare not performed with the calibration strip 240. Rather, thecalibration strip 240 delivers the information, the algorithms, theparameters, and the procedures that are required to characterize anassay to the analyte test instrument 100. The ROM 250 is capable ofstoring and downloading to the analyte test instrument 100 parametersthat characterize an assay as having a two-electrode format or athree-electrode format.

Referring to FIGS. 4A and 4B, a test strip 400 has a pattern ofconductive material 402 on the major surface 404 thereof that does notsupport the electrodes 406. The electrodes 406 are supported on themajor surface 408 of the test strip 400. Different patterns ofconductive material 402 can be used to specify different assays (e.g.,glucose, ketone bodies, etc.). For each different assay, the pattern ofconductive material 402 is disposed in such a way that the electricalcontacts IDENT1, IDENT2, and IDENT3 of the test port 110 interact withthe conductive material in the pattern to identify the type of assaythat will be performed by the test strip 400, such as, for example,glucose, ketone bodies, lactate. A device circuit 212, such as an ASIC(see FIG. 2), identifies the type of assay that will be performed by thetest strip 400 by determining the pattern of connection of theconductive material 402 on the major surface 404 of the test strip 400.

When a strip (e.g., calibration strip, glucose test strip, ketone bodiestest strip, etc.) is inserted into test port 110 of the analyte testinstrument 100, the analyte test instrument 100 detects the presence ofthe strip and performs a procedure to determine whether the strip is acalibration strip or a test strip for determination of the concentrationof an analyte. First, the instrument software 220 polls the test port110 to identify the function of the strip that has been inserted, i.e.calibration strip, test strip for determination of the concentration ofan analyte. In one embodiment, the instrument software 220 attempts tocommunicate with the inserted strip by means of a protocol capable ofoperating with a serial EE-squared interface, such as that defined bythe Dallas ROM protocol of Dallas Semiconductor, Dallas Tex. Such aninterface provides single-wire communication. If the attempt tocommunicate is successful, the instrument software 220 proceeds to theROM calibration procedure. If the attempt to communicate isunsuccessful, the instrument software 220 puts the analyte testinstrument 100 into a brief wait mode (a predetermined time period),e.g., three to five minutes. If the analyte test instrument 100 fails toreceive a signal indicating that a sample has been received during thewaiting period, the analyte test instrument 100 shuts itself offautomatically.

The receipt of a signal by microprocessor 216 indicates that the user isperforming an assay for determination of the concentration of ananalyte. Referring to FIG. 3A, when a test strip 230 is inserted intothe test port 110, the electrical contacts 232 communicate with theanalyte test instrument 100. When a sample (not shown) is added to thereaction area 236, the sample reacts with the reagents in the reactionarea, thereby causing a flow of electrons to produce an electricalresponse, such as a change in current. The response is detectable by theanalyte test instrument 100. The analyte test instrument 100 convertsthe detected signal into data corresponding to information relating tothe analyte and displays the information to the user.

FIG. 5 illustrates the ROM calibration procedure when a calibrationstrip is introduced into the test port 110. When the instrument software220 identifies the calibration strip 240 (step 710), data from the ROM250 is downloaded to the analyte test instrument 100 (step 720). Afterthe data from the ROM 250 has been downloaded to the analyte testinstrument 100, the display 130 displays the lot number downloaded fromthe calibration strip 240 (step 730), as an indication that thecalibration is complete. This data is stored in the memory 218 (step740). The user can then remove the calibration strip from the test port110 (step 750). The downloaded data remains in the memory 218 for use bythe analyte test instrument 110 until a new calibration procedure isperformed (step 760). In some embodiments, the analyte test instrument100 can store more than one set of calibration data in the memory 218.For example, an analyte test instrument 100 capable of performing assayswith a plurality of test strips 230 (e.g., glucose, ketone bodies), canstore a set of calibration data for each type of test strip 230.

As described in U.S. Pat. No. 6,377,894, incorporated herein byreference, the downloaded and stored data comprises parameters,algorithms, operational procedures, and the like for controlling theoperation of the analyte test instrument 100. In a preferred embodimentof this invention, the data comprise information that instructs theanalyte test instrument to perform an assay with a test strip having twoelectrodes or with a test strip having three electrodes. In anotherpreferred embodiment, the data comprise information that instructs theanalyte test instrument 100 to begin an assay in a mode where thecircuitry anticipates a test strip having two electrodes and then switchto a mode where the circuitry is changed to accommodate a test striphaving three electrodes.

Operation

FIG. 6 depicts a flow chart of a method of performing an assay with theanalyte test instrument of this invention. A calibration strip 240 isinserted into the test port 110 and information about types of assays(e.g., glucose, ketone bodies) and the configuration of the test stripcircuit 214 (i.e., two electrodes or three electrodes) are downloadedand stored in the memory 218 of the analyte test instrument 100 (step800). The calibration strip 240 is removed from the test port 110. Atest strip 230 is inserted into the test port 110 (step 810). Themicroprocessor 216 of the analyte test instrument 100 determines whetherthe strip inserted into the test port 110 is a test strip 230 or acalibration strip 240 by transmitting a digital signal along a wire tothe strip. If no signal is received from the strip, the microprocessor216 has determined that the strip is a test strip 230. Themicroprocessor 216 then determines the pattern of electrical contacts onthe major surface of the test strip 230 that does not support theelectrodes (step 820). The aforementioned pattern of electrical contactsprovides a signal to the microprocessor 216 indicating the assay thatcan be performed with the test strip 230 that has been inserted into thetest port 110, such as, for example, a glucose assay, a ketone bodiesassay. The microprocessor 216 then sets the switches of the test stripcircuit 214 to the mode for a test strip having two electrodes (step830). A sample is then introduced to the reaction area 236 of the teststrip 230. A voltage is applied, and after a brief period of time, asmall current can be detected (step 840). The current indicates that asample, which covers the electrodes, has been detected (step 850). Whenthe current is detected, the microprocessor 216 instructs a switch (notshown) in the device circuit 212 to open, thereby disconnecting theelectrodes on the test strip from the test strip circuit 214 for aspecified period of time (step 860), which period has been preset by themicroprocessor 216. After the specified period of time, the switch (notshown) in the device circuit 212 is closed and the test strip circuit214 remains in the two-electrode mode if the test strip is one havingtwo electrodes, or the switches (not shown) in the test strip circuit214 are set for a test strip having three electrodes (step 870) if thetest strip is one having three electrodes. The appropriate electrodemode is determined by the microprocessor 216. The appropriate level ofvoltage is applied, and the current resulting from the electrochemicalreaction between the sample and the reagents on the test strip ismeasured (step 880). The microprocessor 216 then converts the currentmeasured into the appropriate value of concentration of analyte by meansof parameters and algorithms that had been previously supplied by thecalibration strip 240 and stored in the memory 218. The microprocessor216 then instructs the display 130 to show the value of theconcentration of analyte (step 890). Assays for different types ofanalytes and assays employing different types of test strips, i.e., teststrips having two electrodes and test strips having three electrodes,can be carried out on the same analyte test instrument 100. If thecharacteristics of test strip for a particular assay are changed, suchas, for example, a new assay for glucose is developed, the instructionsfor the analyte test instrument can be changed merely by using a newcalibration strip; the analyte test instrument need not be discarded.

FIG. 7A, FIG. 7B, and FIG. 8 illustrate a test strip circuit 214 thatcan be used to perform assays with two different types of test strips—atest strip having two electrodes and a test strip having threeelectrodes. FIG. 7A and FIG. 7B show a top view of a test strip 900having three electrodes, the test strip inserted in the test port 110.The test strip 900 is shown without its insulating coating, whereby aworking electrode 902, a counter electrode 904, and a referenceelectrode 906 are visible. The electrical contacts 908 at the end 910 ofthe test strip 900 are also visible. FIG. 8 shows a top view of a teststrip 900 a having two electrodes, the test strip inserted in the testport 110. The test strip 900 a is shown without its insulating coating,whereby a working electrode 912, a dual-purpose reference/counterelectrode 914, and a trigger electrode 916 are visible. The electricalcontacts 918 at the end 920 of the test strip 900 a are also visible.FIG. 3A shows a test strip 230 having an insulating coating 238 present.In FIG. 7A, the electrical contacts 908 at the end 910 of the test strip900 are shown inserted into the test port 110, where they make contactwith electrical contacts SENS1, SENS2, and SENS3. These electricalcontacts are depicted in FIG. 2. The electrical contacts SENS1, SENS2,SENS3 make electrical contact with the active electrical components ofthe test strip circuit 214 through wires 922, 924, and 926,respectively. The wires 922 and 924 have switches 928 and 930,respectively, controlled by the microprocessor 216, located between theelectrical contacts (not shown) of the test port 110 and the test stripcircuit 214. The switches 928 and 930 are used to connect or disconnectthe electrical contacts SENS1 and SENS3 from the test strip circuit 214.FIG. 7A also shows operational amplifiers 932 and 934; resistors 940,942, and 944; microprocessor-controlled switch 946; twoanalog-to-digital (ND) converters 950 and 952; and two digital-to-analog(D/A) converters 954 and 956. The microprocessor 216 shown in FIG. 7A ispart of the processing circuit 210. The processing circuit is shownschematically in FIG. 2.

The test strip circuit 214 is first set in the two-electrode mode by themicroprocessor 216. FIG. 7A shows switch 946 set in the two-electrodemode. The working electrode 902 is disconnected from the test stripcircuit 214 by means of a microprocessor-controlled switch 928 in thewire 922. The D/A converter 956 receives a digital voltage instructionfrom the microprocessor 216 and applies an analog voltage, 400 mV,between the counter electrode 904 and the reference electrode 906 bymeans of the operational amplifier 932. The microprocessor 216 continuesto interrogate the A/D converter 952. When a sufficient quantity of thesample is applied to the test strip 900 to result in a fluid connectionbetween the counter electrode 904 and the reference electrode 906, acurrent begins to flow between the two electrodes. When the currentreaches a threshold, e.g., 0.5 microamperes, the microprocessor 216opens the switch 930 in the wire 924 leading to the reference electrode906 for a short period of time, e.g., from about 0 to about 10 seconds.The next instructions from the microprocessor 216 differ, depending onwhether the assay employs a test strip having two electrodes or a teststrip having three electrodes.

If the assay involves a test strip employing three electrodes, theswitch 946 is set at shown in FIG. 7B. The microprocessor-controlledswitches 928 and 930 in the wires 922 and 924, respectively, are closed.The D/A converter 954 receives a digital voltage instruction from themicroprocessor 216 and applies an analog voltage, 200 mV, to the workingelectrode 902 by means of the operational amplifier 934. The currentoriginating at the working electrode 902 as a result of the reaction ofthe sample with the reagent is converted by the A/D converter 950 to adigital signal that is received by the microprocessor 216. Themicroprocessor 216 receives the digital signal from the A/D converter950 at a specific time or at specific times. The microprocessor 216 canreceive data from the ND converter 950 at more than one time window, andthe data from the different time windows can be used to perform errorchecks on the assay. Typical time windows for the microprocessor 216 toreceive data are 4 to 5 seconds and 8 to 10 seconds. The microprocessor216 uses the digital signal to calculate a concentration of analyte inthe sample by using calibration factors supplied by a calibration strip.The concentration can then be displayed on the display 130 of theanalyte test instrument 100.

If the assay employs a test strip having two electrodes, the switch 946remains in the position shown in FIG. 8. The test strip circuit 214 isfirst set in the two-electrode mode by the microprocessor 216. FIG. 8shows the switch 946 set in the two-electrode mode. The workingelectrode 912 is disconnected from the test strip circuit 214 by meansof the microprocessor-controlled switch 928 in the wire 922. The D/Aconverter 956 receives a digital voltage instruction from themicroprocessor 216 and applies an analog voltage, 400 mV, between thetrigger electrode 916 and the dual-purpose reference/counter electrode914 by means of the operational amplifier 932. The microprocessor 216continually interrogates the D/A converter 952. When a sufficientquantity of sample is applied to the test strip 900 a to result in afluid connection between the fill trigger electrode 916 and thedual-purpose reference/counter electrode 914, a current begins to flowbetween the two electrodes. When the current reaches a threshold, e.g.,0.5 microamperes, the microprocessor 216 opens the switch 930 in thewire 924 leading to the trigger electrode 916 for a short period oftime, e.g., from about 0 to about 10 seconds. Because the assay employsa test strip having two electrodes, the switch 946 remains in theposition shown in FIG. 8. The microprocessor-controlled switch 928 inthe wire 922 is closed. The D/A converter 954 receives a digital voltageinstruction from the microprocessor 216 and applies an analog voltage,200 mV, to the working electrode 912 by means of the operationalamplifier 934. The current originating from the working electrode 912resulting from the reaction of the sample with the reagent is convertedby the ND converter 950 into a digital signal that is received by themicroprocessor 216. The microprocessor 216 receives the digital signalfrom the A/D converter 950 at a specific time or at specific times. Themicroprocessor 216 can receive data from the A/D converter 950 at morethan one time window, and the data from the different time windows canbe used to perform error checks on the assay. Typical time windows forthe microprocessor 216 to receive data are 4 to 5 seconds and 8 to 10seconds. The microprocessor 216 uses the digital signal to calculate aconcentration of analyte in the sample by using calibration factorssupplied by a calibration strip. The concentration can then be displayedon the display 130 of the analyte test instrument 100.

FIGS. 7A, FIG. 7B, and FIG. 8 demonstrate that the same test stripcircuit 214 can be used to analyze test strips having either twoelectrodes or three electrodes. The analyte test instrument of thisinvention is therefore more versatile than analyte test instruments ofthe prior art. The analyte test instrument of this invention canidentify the type of test strip inserted into the instrument (i.e., onehaving two electrodes or one having three electrodes), and, by usingstored calibration information, can configure the analyte testinstrument appropriately without relying on input from the user. Theanalyte test instrument of this invention is therefore easier for theuser to switch from one circuit to another than are analyte testinstruments of the prior art.

The test strip circuit of the analyte test instrument of this inventionand the method wherein a two-electrode mode is employed at the beginningof the assay to detect when the test strip is filled allows measurementsto be made with much less expensive operational amplifiers, therebyreducing the cost of the analyte test instrument while providingperformance characteristics of expensive analyte test instruments.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

1-46. (canceled)
 47. A method for performing an assay using an analytetest instrument, the analyte test instrument comprising: a test port forreceiving a test strip; a microprocessor for executing instructionsdownloaded to the analyte test instrument; and a test strip circuit thatswitches between a two electrode configuration and a three electrodeconfiguration following sample application to the test strip and beforeremoval of the test strip, wherein switching between the configurationscomprises the microprocessor setting the switches of the test stripcircuit from an assay with a test strip having two electrodes to anassay with a test strip having three electrodes or the microprocessorsetting the switches of the test strip circuit from an assay with a teststrip having three electrodes to an assay with a test strip having twoelectrodes, wherein the test strip circuit is in a two electrodeconfiguration during a first portion of an assay and a three electrodeconfiguration during a second portion of the assay, wherein the methodcomprises: inserting a test strip into the test port of the analyte testinstrument, wherein the test strip circuit of the analyte testinstrument is in a two electrode configuration; after inserting the teststrip, applying a sample to the test strip; running a first portion ofan assay on the sample applied to the test strip; switching the teststrip circuit of the analyte test instrument from the two electrodeconfiguration to a three electrode configuration; running a secondportion of the assay on the sample applied to the test strip; and afterrunning the second portion of the assay, removing the test strip fromthe test port.
 48. The method according to claim 47, wherein the testport is configured to receive a calibration strip, which calibrationstrip is removable from the test port to allow a test strip to beinserted into the test port, and wherein the method comprisescalibrating the analyte test instrument using a calibration strip priorto inserting the test strip into the test port.
 49. The method accordingto claim 47, wherein the analyte test instrument is configured todetermine the concentration of an analyte in the sample, and wherein theassay is an analyte concentration determining assay.
 50. The methodaccording to claim 49, wherein the analyte is selected from the groupconsisting of: glucose, a ketone body, and lactate.
 51. The methodaccording to claim 50, wherein the analyte is glucose.
 52. The methodaccording to claim 49, wherein the analyte test instrument comprises adisplay, and wherein the method comprises displaying a determinedanalyte concentration on the display.
 53. The method according to claim52, wherein the method comprises displaying one or more messages to auser of the analyte test instrument.
 54. The method according to claim53, wherein the displaying comprises displaying a warning message to auser of the analyte test instrument.
 55. The method according to claim47, wherein the analyte test instrument comprises a memory for storinginstructions and information.
 56. The method according to claim 55,wherein the memory is configured to store results of one or more assaysperformed using the analyte test instrument.
 57. The method according toclaim 56, comprising enabling a user of the analyte test instrument torecall and display the results of the one or more assays.
 58. The methodaccording to claim 47, wherein the analyte test instrument comprisessoftware configured to generate menus accessible by a user of theanalyte test instrument, and wherein the method comprises providing theuser access to the menus.
 59. The method according to claim 47, whereinthe analyte test instrument is configured to transmit data to one ormore external devices, and wherein the method comprises transmittingdata to one or more external devices.
 60. A method of performing aglucose concentration determining assay using a glucose test instrument,the glucose test instrument comprising: a test port for receiving aglucose test strip; a microprocessor for executing instructionsdownloaded to the glucose test instrument; and a test strip circuit thatswitches between a two electrode configuration and a three electrodeconfiguration following sample application to the test strip and beforeremoval of the test strip, wherein switching between the configurationscomprises the microprocessor setting the switches of the test stripcircuit from an assay with a test strip having two electrodes to anassay with a test strip having three electrodes or the microprocessorsetting the switches of the test strip circuit from an assay with a teststrip having three electrodes to an assay with a test strip having twoelectrodes, wherein the test strip circuit is in a two electrodeconfiguration during a first portion of an assay and a three electrodeconfiguration during a second portion of the assay, wherein the methodcomprises: inserting a glucose test strip into the test port of theglucose test instrument, wherein the test strip circuit of the glucosetest instrument is in a two electrode configuration; after inserting theglucose test strip, applying a sample to the test strip; running a firstportion of a glucose concentration determining assay on the sampleapplied to the test strip; switching the test strip circuit of theglucose test instrument from the two electrode configuration to a threeelectrode configuration; running a second portion of the glucoseconcentration determining assay on the sample applied to the test strip;and after running the second portion of the glucose concentrationdetermining assay, removing the test strip from the test port.
 61. Themethod according to claim 60, wherein the test port is configured toreceive a calibration strip, which calibration strip is removable fromthe test port to allow a test strip to be inserted into the test port,and wherein the method comprises calibrating the glucose test instrumentusing a calibration strip prior to inserting the glucose test strip intothe test port.
 62. The method according to claim 60, wherein the glucosetest instrument comprises a display, and wherein the method comprisesdisplaying a determined glucose concentration on the display.
 63. Themethod according to claim 62, wherein the method comprises displayingone or more messages to a user of the glucose test instrument.
 64. Themethod according to claim 63, wherein the displaying comprisesdisplaying a warning message to a user of the glucose test instrument.65. The method according to claim 60, wherein the analyte testinstrument comprises a memory configured to store results of one or moreglucose concentration determining assays performed using the glucosetest instrument, and wherein the method comprises enabling a user of theglucose test instrument to recall and display the results of the one ormore glucose concentration determining assays.
 66. The method accordingto claim 60, wherein the glucose test instrument is configured totransmit data to one or more external devices, wherein the methodcomprises transmitting data to one or more external devices.